I've had a dropper bottle in my cabinet for about four years. It's barely half empty as I am an extreme over-responder, taking only a single drop twice per week.
Does the stuff go bad? Does it lose potency or turn rancid or both?
I've heard its useless after 6 months...there may be some of it left in there that is effective, but you have no idea what the potency is at this point...I'd probably toss it and get a new bottle...its pretty cheap..